Studies will be carried out in attempts to gain some insight into the mechanism involved in the regulation of the humoral immune response once it has been initiated. The model to be studied will be the response of rabbits to aggregated preparations of human IgG (AHulaG). Experiments will be designed to investigate the possible role of suppressor T cells in the cyclical appearance of both plaque forming cells and antibody following intravenous injection of AHulaG. The role of the thymus in the cyclical pattern will be investigated with the use of adult rabbits thymectomized during early life. Other studies will attempt to determine the role of the C3 component of complement in regulation of the response to AHulgG in rabbits. Experiments are designed to determine if the disruption of the cyclical pattern resulting from C3 depletion is the result of the failure of antigen localization in splenic follicles. Attempts will be made to correlate the cyclical pattern of the response of rabbits to AHulgG with the ability of spleen cells taken at various times post injection to respond in vitro. Other experiments are planned to investigate the role of the Fc region on the regulation of the immune response to AHulgG in both mice and rabbits. Attempts will be made to improve procedures for obtaining highly enriched preparations of HuIgG specific B cells from primed mice. BIBLIOGRAPHIC REFERENCES: Romball, C.G. and Weigle, W.O. Modulation of regulatory mechanisms operative in the cyclical production of antibody. J. Exp. Med. 143:497, 1976. Romball, C., R. Ulevitch, and W. Weigle. Effect of C3 depletion on the in vivo response in rabbits to a thymus-dependent antigen. Fed. Proc. 36:1289, 1977.